I know this post is too old, but since it shows up in google search on "histignore", I have to add, that there's more-- em, 'built-in' way of ignoring commands that start with " ". So, instead of adding "[ \t]*" to HISTIGNORE, you can use HISTCONTROL=ignorespace.

But actually I don't know if it makes any difference. Just makes your .bashrc more readable.